Please someone, what's wrong?

Expecting the drain of M2 to move from about 0v to 6v but not working

Thanks

@Dodgydave

 

Post a circuit so we can all see it.

 

DISREGARD THE FOLLOWING. TOO EARLY IN THE MORNING, NOT ENOUGH COFFEE.

Expecting the drain of M2 to move from about 0v to 6v but not working

What constitutes "working"? What did you expect this circuit to do?

Your circuit will either sit there with the output of U1 at 1/2 of Vcc, or it will sit there with the output of U1 at 1/4 of Vcc, depending on the Vgs(thr) of M2 (which can range from 0.8 volts to 3.0 volts).

It won't do anything else.

 

I don't have a model for 2N7000, but with the 'nmos' model it does oscillate.

 

I'm guessing that your supply must be 6V?
I don't know why it shouldn't work. You should get a vaguely triangular wave at the junction of C1/R1 with a negative peak of 1.5V and a positive peak of 3V; and a 6V/0V squarewave on the output of the AD822 at about 3.8kHz.
What IS it doing? What are the DC voltages that it is stuck at?
Why did you include M1, M2 and R2 - you could have connected R5 directly to the AD822 output? That would make it the standard comparator relaxation oscillator (same principle as a 555).
Why are you using a £9 op-amp to do the same job as a 25p timer?

 

Please someone, what's wrong?

Expecting the drain of M2 to move from about 0v to 6v but not working

See this file:

 

I see the Vcc voltage source in the bottom right corner now. It's 12V. The drain of M2 will got to Vcc when M2 is off.
If you want a 0-6V output, then make Vcc 6 Volts.
Why did you expect it to go to 6V?

 

Please what's wrong with this?

The circuit on the right in file

Expecting the cap to oscillate between 3 and 8V

Vcc is 12V

Thanks

 

1) It's not the same circuit you posted 2 months ago.
2) It's not the same design you have in your attached .asc file.
3) Voltage at C1 in the latter file does oscillate as you expect.

 

1) It's not the same circuit you posted 2 months ago.
2) It's not the same design you have in your attached .asc file.
3) Voltage at C1 in the latter file does oscillate as you expect.

3) C2...The circuit on the right

Thanks